1. Field of the Invention
This invention is for processing of recycled asphalt pavement or virgin asphalt where the mixture contains recycled rubber. The Federal Highway bill (ISTEA) enacted in December 1992 requires each state to use asphalt pavement containing asphalt rubber in 5% the total tons of asphalt pavement laid in the state and financed in whole or in part by Federal funds. The required percentage of asphalt pavement containing recycled rubber, in relation to the total tons of asphalt laid in each state, increases by 5% each year until reaching 20% in 1997.
The Federal Highway Bill mandate requires that there be threat to human health or the environment, that the asphalt containing rubber must be recyclable and that the performance of the rubber containing asphalt pavement must be equivalent to that of existing hot-mix pavements.
The accumulation of used tire carcasses has become a substantial environmental problem. A need has therefore developed to dispose of old tire carcasses, and incorporation of the tire rubber into hot-mix asphalt provides an attractive solution.
2. Description of the Prior Art
In the prior art, reprocessed rubber from automobile tires has been used in various mixtures to form paving material for roads.
U.S. Pat. No. 3,915,581, Copp, Jr., teaches the use of shredded or powdered automotive tires which is processed to be suitable for vulcanizing. This utilization of reprocessed rubber is directed to rubber pavement, contains a high percentage of used rubber and is not a component of hot-mix asphalt.
U.S. Pat. No. 2,952,650, Wood, teaches the use of a rubber powder and incorporation of the rubber powder in the amount of generally 1 to 20% of the asphalt content. In this process, butyl rubber is masticated at elevated temperatures with a rubber plasticizer, carbon black and vulcanizing ingredients until the rubber vulcanizes. The contemplated rubber, however, is not used automobile tire. The use of a rubber plasticizer similar to the asphalt used in roads and having a penetration value from 40 to 300 is suggested. The rubber processing oil may be an aromatic, napthanic or asphaltic rubber softening oil.
U.S. Pat. No. 3,915,581, Copp, Jr., teaches the use of a rubber paving material. In this disclosure, the author recommend against adding shredded or ground rubber to a binder, and that the rubber be reprocessed into a vulcanizing state and applied as a solid rubber paving.
U.S. Pat. No. 3,253,521, Endres, teaches a rubberized bitumen particulated rubber. An adhesive composition for the rubbery asphalt is disclosed as containing 3% of rubber and 97% of 85/100 penetration asphalt on a weight basis. The microscopically dispersed rubber in the bitumen is disclosed as being between 2% and no more than 10%.
U.S. Pat. No. 2,977,864 is another example of a rubberized asphalt which may contain 2% weight by rubber. Rubber pellets are heated to a temperature of 250.degree. F. and then placed in a pug mill mixer and mixed fine rubber particles.